Recovery of nickel from nickel silicate ore



Patented Oct. 30, 1951 RECOVERY OF NICKEL FROM NICKEL SILICATE ORE Lyall J. Lichty, Ottawa, Ontario, Canada, assignor to Quebec Metallurgical Industries Limited, Toronto, Ontario, Canada, a corporation of Canada No Drawing. Application October 30, 1950, Serial No. 193,031

i Claims.

The present invention relates to a method for recovering substantially all the nickel in the form of a high nickel content ferro nickel alloy from nickel silicate ores containing a,,small amount of nickel and a relatively large amount of iron.

Nickel silicate ores are complex silicates the composition of which varies depending .upon the location of the deposit from which they are obtained. In addition to nickel they usually contain a large amount of iron and either aluminum or magnesium or both in substantial amount. The nickel silicate mines of most commercial importance today are those of New Caledonia, the nickel mineral of which is garnierite. Its approximate analysis is 5 to 6' per cent nickel, 14 per cent F6203, 15 per cent MgO, 43 per cent S102 and per cent combined water. The laterite ores, such as occur in Cuba, are lower in silica but higher .in iron content. The term silicate ore as used herein is intended to include the laterite ores.

The conventional practice for recovery of nickel from high grade ore, such as the New Caledonia ore comprises first smelting in a blast furnace with gypsum to produce a nickel-iron matte with 30 to 45 per cent nickel. This is treated in a converter to remove iron and part of the sulphur leaving nickel sulphide. The converter slags are rich in nickel and must be resmelted. The nickel sulphide is roasted to produce oxide and the oxide may be reduced.

Low grade and medium nickel silicate ores contain less nickel and usually more iron. Due principally to the high ratio of iron to nickel in these ores, it has not been economical to process them by the conventional practice of smelting with gypsum and converting. So far as I am aware no satisfactory method has been proposed for the recovery of nickel in a commercial useable metallic form from low grade or medium grade nickel silicate ore.

The present invention is based upon discoveries made in smelting low 'andmedium grade nickel silicate ores with a flux, such as lime, and an alloy of silicon, aluminum and iron as a reducing agent which is predominately silicon. In these ores the ratio of iron to nickel is greater than about 3.0 and the nickel content usually is between 1.5-to 3.0 per cent but may be as'low as 0.75 per cent. I have discovered that as the amount of reducing agent used with a fixed amount of ore is diminished progressively below the amount theoretically required to reduce all the iron'and nickel in the ore to metal, (1) a series of ferro-nickel alloys is obtained containing a progressively greater percentage of nickel and a progressively smaller percentage of iron; (2) in this series of alloys the amounts of nickel in those containing between about 30 to 60 per cent nickel by weight are substantially equal to the amount of nickel in the amount of ore treated, that is, the recovery of nickel is about 95 per cent; and (3) the alloys containing about 30 per cent or more are free of silicon. With some ores I have found that the percentage recovery of nickel begins to decrease as the amount of nickel in the ferro-nickel produced is increased over about 50 per cent and when the nickel content of the ferro-nickel is 60 per cent, the percentage nickel recovery is reduced to about 85 per cent.

The present invention involves smelting a low grade or medium grade nickel silicate ore with an amount of a reducing agent of the type specified herein selected to produce a ferro-nickel alloy containing more than about 30 per cent nickel and, preferably, not more than about 60 per cent nickel. While my investigations have been confined to the treatment of low or medium grade ore, I believe the invention is applicable to other nickel silicate ores in which the ratio of iron to nickel is substantially greater than that in the ferro-nickel alloy desired to be produced.

The advantages of the invention are two-fold. Thus, the invention (1) provides a method for the efiicient recovery of the valuable nickel component' from nickel silicate ores and (2) produces directly a high nickel content and high purity useful commercial product adapted for many uses previously requiring cathode nickeL' In view of the small amount of reducing agent used with such a relatively large volume of ore containing a small" amount of nickel and a relatively large amount of reducible iron compound which has a strong afiinity for the reducing agent, it is surprising to discover that substantially all the nickel of the ore can be recovered in a high purity ferro-nickel containing more than 30 per cent nickel.

In the practice of the invention, I may employ as the reducing agent either silicon or ferrosilicon, aluminum or an alloy of silicon, aluminum and iron known as alsifier. I presently prefer to employ an alloy, a typical analysis of which is silicon 66.5 per cent, aluminum 8 per cent and iron 25 per cent, produced by reducing in an electric furnace a charge containing 6 to 20 per cent iron oxide,r3 to 25' per cent aluminum oxide,

40 to 55 per cent silica and carbon between to 100 per cent of the amount theoretically required to reduce all the oxides in the charge to metal.

To obtain the advantageous results described above, it is necessary *to employthe'reducin agent inthe'form of a fine powder. :Ichavesfound that the particle size of the reducing agent should not exceed about 65 mesh. It also is necessary to obtain an intimate mixture .between the ore and the reducing agent. I have obtainedmrost satisfactory results by intimately mixing the finely divided reducing agentwithrpulverizediore before they are introduced into the furnace. When reducing small batches of "ore"I have"obtained best results employing an ore pulverized to about 10 mesh but when the .ore is .reduced in large batches it may be used in lumpssup .1130 one inch or more in size. I also intimately mix a flux, such as lime, with the ore to'provi'de'a fluid slag and to reduce the melting temperature of the chargapreferably, to between1ab'out1I40'0" C. and 1500 C. but a. higher temperature may) be used if desired. The'mixture of pulverized :ore,

'flux:and finely dividedrreducingsagent is placed in a-suitable furnace, such. as an oiltfiredrfurna'ce or anelectric furnace of'the 'electrode'typa; and melted. :zDuring melting thenickel component and azportion of the iron component-zofithexore are reducedto form=a molten ferro-nickehalloy which sinks to the :bottomof'thefurnacebeneath a molten'slag and mayi'be'tapped In thepractice of the inventionIhavez'found one pound of reducing agent containing about 25 per cent iron-and the remainder'essentially silicon or silicon'an'd aluminum, will produce approximate y three pounds 'of ferro-nickelsalloy. In computing the amount of such reducing agent required to produce a 'ferro-nickelalloy containing more than 30 per cent of nickel'or a desired amountof nickel between 30 and: 60 per:cent,.it is practical and convenient to employ the "formula his 31/ whereia: is-the' weight of nickel. in" the amount of ore :beng treated "and -y is an integer not less than 30. lInzthisformula the integer used corresponds to the 'des'red per-cent of-nickel in-1the ferro-nickelalloyto be produced. Thus, if it is desired to produce a vferro-nickel alley containing' approxima ely 40 per cent"nickel;ithe' integer used is140. If the amount of iron in the'reducin agent'used. is substantially'more or" less thant2'5 percent, the amount required, as computed-by the-above formula. should be increased percent for each *per cent variation inironcontent of the reducim agentfrom 'per cent.

Insome instances, the-nickel si icate ore may contain .-asmall amount of a-copper' or.a.cobalt component .orboth. Insuch instances, the .copper orcobalt componentor both will be reduced and alloy with the .ferro-nickel alloypro'duced. For most uses of-theferro-nickel alloy the presence of cobalt is not objectionable. The presence of copper in the product in .the ratio of about 021? part to sixty parts "of nickel is 'notobjectiona e.

In some instances, a small amount'o'f sulfur component may be present in the ore andmay be reduced and "enter the alloy-produced. In such event, the alloy can be 'desulfurized if desired by known methods.

The practice of the invention is illustrated further by therolowing-specific examples of the treatmenttof ores obtained from difierentllqqelities.

Example 1 Five hundred pounds of raw New Caledonia nickel silicate ore containing 2.27 per cent nickel, 14411 per cent iron, 42I6 per cent silica, 19.02 per cent magnesia,'1.67 per cent alumina, 2.39 per cent lime, 0.83 per cent chromium, 0.17 per cent "manganese, a trace of copper and with a substantial loss on ignition, was mixed with pounds of lime and 8.9 pounds of reducing agent containing 66.5 per cent silicon, 8 per cent 'aluminum,25 per:cent iron and minor amounts .of-other:metals. After melting the mixture at a temperature of approximately 1500 C., in a suitable furnace, and allowing the melt to settle,

Where was obtained 25.4 pounds of ferro-nickel "containing 42.32 per cent nickel, 0.02 per cent Example 2 "Four "hundred pounds of Celebesnickel ore containing 2.38 per cent nickel, 0.04 per cent sulfur, 10.02 percent iron, 42.24 per cent .silica, 2.72 per cent alumina,..22'.30 per cent magnesia, 0.62 per cent chromium, 0.13 per cent manganese and with a substantial loss 'on'ignition wasmixed with120pounds burnt lime and 7.5 poundsreducing agent containing 66.5 per cent silicon, 8 percent aluminum, 25 per cent iron and minor amounts'of other metals. After, melting the mixture in a suitable furnace at a temperature of 1500 'C., andallowing themelt to settle, there was .obtainedi22;6 pounds ferro-nickel containing 4011 per cent nickel, 0.07 per cent copper, 0.145 per cent sulfur, 0.05 per cent carbon, 0.044per cent phosphorus, 0.005 per cent chromium, a trace of .silicon and manganese, and the balance iron. The recovery of nickel was about per cent. In addition, there was obtained 564pounds of slag containin .0.08.per cent nickel and the remaining non-volatile constituents of the original mixture.

Example 3 :Four hundred pounds'of Celebes nickel ore.con taining 2.38 per cent nickel,.0.0.4*per cent sulfur, 10.02 "per cent iron, 4224 per cent silica, .2172 pericent'alumina, 22.30 per:cent magnesia, (162 percent chromium, 0.131per cent-manganese and with a substantial loss on ignition, was mixed withr poundsof burntlimeand5 poundsof reducing agentcontaining 66.5 per cent'silicon, Bper-centraluminum, 25 per cent iron, and minor amounts of. other metals. .After melting the: mixturein suitable furnace at a temperature of about 1500 0., and allowing the melt to settle, there was obtained '13.1 pounds of ferro-nickel contaming- 61333 per cent nickel, 0.03per cent copper, 0.14 per 'cent'sulfur, 0103 per cent carbon, 0.02-percent phosphorus, 0.005 per cent chromium and traces of silicon and manganese. The recovery or nickel was about 84 per cent. In addition there was obtained'a slag containing 0.31 percent nickel and'the remaining non-volatile constituents of the original mixture.

1 claim:

'1. The method which comprises intimately mixing -a=pulverized nickel silicate ore with a 'fiux 'and :a reducing agent .selected from the con and an alloy of silicon, aluminum and iron and having a particle size not greater than about 65 mesh, the ratio of iron to nickel in said ore being not less than about 3.0, the amount of reducing agent being substantially equal to plus 5 per cent thereof for each 10 per cent variation in iron content of the reducing agent from 25 per cent where x is the weight of nickel in the amount of ore treated and y is an integer between 30 and 60, thereafter supplying heat to melt the mixture whereby substantially all the nickel component and a portion only of the iron component of the ore are reduced to metal to form a molten ferro-nickel alloy containing not less than about 30 per cent nickel which settles beneath a molten slag, and separating the ferronickel alloy from the slag.

2. The method which comprises intimately mixing a pulverized nickel silicate ore with a reducing agent and flux, said reducing agent being an alloy of silicon, iron and aluminum and having a particle size not greater than about 65 mesh, the amount of reducing agent being substantially equal to E 1 3. plus 5 per cent thereof for each per cent variations in iron content of the reducing agent from 25 per cent where a: is the weight of nickel in the amount of ore treated and y is an integer between 30 and 60, the ratio of iron to nickel in said ore being not less than about 3.0, there after supplying heat to melt the mixture whereby substantially all the nickel component and a portion only of the iron component of the ore are reduced to metal to form a molten ferronickel alloy containing not less than about 30 per cent nickel which settles beneath a molten slag, and separating the ferro-nickel alloy from the slag.

3. The method which comprises mixing a pulverized nickel silicate ore with a flux to reduce the melting temperature of the ore, supplying heat to melt the mixture, intimately mixing with said mixture a reducing agent selected from the group consisting of silicon, aluminum, ferrosilicon and an alloy of silicon, aluminum and iron and having a particle size not greater than about 65 mesh, the ratio of iron to nickel in said ore being not less than about 3.0, the amount of reducing agent being substantially equal to ation in iron content of the reducing agent from 25 per cent where :c is the weight of nickel in the amount of ore treated and y is an integer between 30 to 60 whereby substantially all the nickel component and a portion only of the iron component of the ore are reduced to metal to form a molten ferro-nickel alloy containing not less than about 30 per cent nickel which settles beneath a molten slag, and separating the ferronickel alloy from the slag.

4. The method which comprises mixing a pulverized nickel silicate ore with a flux to reduce the melting temperature of the ore, supplying heat to melt the mixture, intimately mixing with said mixture a reducing agent consisting of an alloy of silicon, aluminum and iron and having a particle size not greater than about mesh, the ratio of iron to nickel in said ore being not less than about 3.0, the amount of reducing agent being substantially equal to @2 y plus 5 per cent thereof for each 10 per cent variation in iron content of the reducing agent from 25 per cent where a: is the weight of nickel in the amount of ore treated and y is an integer between 30 to 60 whereby substantially all the nickel component and a portion only of the iron component of the ore are reduced to metal to form a molten ferro-nickel alloy containing not less than about 30 per cent nickel which settles beneath a molten slag, and separating the ferro-nickel alloy from the slag.

5. The method which comprises mixing a pulverized nickel silicate ore with lime to reduce the melting temperature of the ore, supplying heat to melt the mixture, intimately mixing with said mixture a reducing agent selected from the group consisting of silicon, ferrosilicon, aluminum and an alloy of silicon, aluminum and iron and having a particle size not greater than about 65 mesh, the ratio of iron, to nickel in said ore being not less than about 3.0, the amount of reducing, agent being substantially equal to plus 5 per cent thereof for each 10 per cent variation in iron content of the reducing agent from 25 per cent where a: is the weight of nickel in the amount of ore treated and y is an integer not less than 30 whereby the nickel and iron components of the ore are reduced to metal to form a molten ferro-nickel alloy containing more than about 30 per cent nickel which settles beneath a molten slag, and separating the ferronickel alloy from the slag.

' LYALL J. LICI-ITY.

No references cited. 

1. THE METHOD WHICH COMPRISES INTIMATELY MIXING A PULVERIZED NICKEL SILICATE ORE WITH A FLUX AND A REDUCING AGENT SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, SILICON, FERROSILICON AND AN ALLOY OF SILICON, ALUMINUM AND IRON AND HAVING A PARTICLE SIZE NOT GREATER THAN ABOUT 65 MESH, THE RATIO OF IRON TO NICKEL IN SAID ORE BEING NOT LESS THAN ABOUT 3.0, THE AMOUNT OF REDUCING AGENT BEING SUBSTANTIALLY EQUAL TO 